The invention is related to the automation of direct drive cut-off knives having cut-to-mark control. A direct drive cut-off machine is one in which the cyclic speeds of the cut-off knives are electronically controlled. The knives cut a continuous web of pre-printed corrugated board into sheets or "blanks".
In particular, this invention is related to the control of such knives to effect automatic order change and/or automatic synchronization of the knives to the registration marks following a transition in the web such as a splice. The knives cut the web at or in reference to the registration marks which are spaced corresponding to the desired sheet length.
The knives are slaved to an optical sensor, which detects presence or absence of the registration marks, and a logic control which synchronizes the knives to the registration marks so as to cut the web at or in specific relation to the registration marks. The logic control periodically enables the optical sensor to scan a narrow portion of the web edge for a registration mark over a short period of time known in the art as a "window". The "window" is intended to prevent the optical sensor from producing spurious signals caused by pre-printed material or blemishes on the web which might otherwise be mistakenly identified as a registration mark.
Heretofore, operating in the cut-to-mark mode, intervention by an operator was necessary when the web was formed of one or more webs connected by a splice and either (1) a roll-to-roll change had occurred within an order wherein the spacing between registrations marks was preserved on both sides of the splice but the spacing between marks was lost across the splice, or (2) an order change was required wherein the spacing between registration marks changed from one order to another across the splice, requiring the cut-off knives to cut sheets of different lengths on each side of the splice.
Operator intervention is necessitated when there has been an order change or a roll-to-roll change within an order because the cut-off knives will normally not be in synchronization with the registration marks of the web following the splice. The registration marks following the splice do not appear in the optical sensor "windows" generated by the logic control since the "windows" are generated based on the spacing between marks preceding the splice. The operator must depress an upstream or downstream adjust button to cause the logic control to synchronize the knives to the registration marks on the web following the splice. This manual adjustment is time consuming and results in the temporary cutting of sheets of improper length, producing scrap and an exceptionally long sheet which may obstruct the sheet-stacking mechanism.
In addition, for an order change it is necessary to sever the web at the splice to separate the old and new orders, and for a roll-to-roll change it is necessary to sever the web at the splice to permit the cut-off knives enough time to "cock" in preparation for the first cut of the new roll web. Severance of the web must be initiated manually. The operator observes the splice as it approaches the shear and presses a button to fire a shear control which causes the shear knives to sever the web. Typically, a splice is missed by several feet using this technique, resulting in wasted board.
The present invention obviates (1) an operator-initiated upstream or downstream adjust for an order change or a roll-to-roll change, and (2) manual-initiated firing of the shear, in the cut-to-mark mode.
The present invention automates synchronization of the cut-off knives with the registration marks of the web following the splice in a manner that mininizes scrap and reduces the possibility of an exceptionally long scrap sheet which obstructs the sheet-stacking mechanism.